The present invention relates to an apparatus for casting steel sheets, particularly those having thin cast cross sections with a thickness down to a lower limit of about 30 mm and a width of about 500 to 1500 mm, in a continuous casting mold equipped with comoving mold walls which are composed of pairs of oppositely disposed endless casting belts and endless lateral dams and define a casting cavity into which the mouthpiece of a tubular casting nozzle extends.
Continuous casters equipped with comoving mold walls (i.e. moving in the casting direction) are presently being used with success for casting lead, zinc and copper at high casting rates around 10 m/min, with the metal melt being introduced into the casting cavity through a trough.
The two lateral dams serving as lateral limitations pass along the continuous casting mold in an essentially straight line; that is, their mutual spacing decreases only slightly in the casting direction for compensation of the shrinkage as a result of solidification of the cast sheet.
The casting of steel of a sufficiently good metallurgical quality requires continuous casters equipped with comoving mold walls in which the entrance of air is avoided in that they are equipped with tubular, i.e. closed, casting nozzles. Such nozzles additionally permit casting under pressure, thus eliminating undesirable fluctuations in the casting level within the casting mold and permitting uniform, symmetrical cooling of the cast product. To be able to roll this cast product under economical conditions, it is necessary to have available material which, with a width of 500 to 1500 mm thickness does not, as previously, have a thickness of 150 to 250 mm, but rather has a thickness which lies only in the order of magnitude of from 30 to 50 mm.
The correct introduction of steel in view of the seal required between parts that move relative to one another (casting nozzle, mold walls), while at the same time avoiding freezing and undesirable solidification in the region of the mouthpiece of the casting nozzle, is very difficult to realize with a billet-type cross section (for example, those having a width of 180 mm) and necessitates the maintenance of the most uniform possible, tight seal between the nozzle mouthpiece and the moving mold walls. Casting of sheet cross sections, for example, those having a width between 500 and 1500 mm, is possible only at added expense because of the correspondingly enlarged dimensions of the casting nozzle which correspond approximately to those of the cast product. Moreover, the enlarged dimensions involve an increased danger of deformation of the casting nozzle and higher material costs for the casting nozzle which consists, for example, at least partly of boron nitride.